'Resistant' starches heal the colon, prevent cancer

Resistant starches thicken the linings of the bowels, allowing for more good bacteria to grow and help with digestion.

By: Christopher Wanjek, LiveScience

February 28, 2013, 1:25 p.m.

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Beans and peas are two sources of resistant starch in a hot dish while rice and pastas offer the benefit only at room temperature. (Photo: GLYPHstock/Shutterstock)

The Borg had it wrong. Resistance is not futile. In fact, it can stave off colon cancer and ease inflammatory bowel disease and other digestion problems.

The resistance, in this case, comes in the form of so-called resistant starches, certain kinds of carbohydrates that resist digestion in the small intestine and enter into the large intestine, or colon, mostly in the same form they entered your mouth.

These starches — found in seed hulls, parts of corn and beans, and in room-temperature rice and pasta — can ferment in the colon to promote the growth of "good" bacteria and have many other beneficial effects.

Researchers at the University of Colorado Denver summarize these benefits in a review paper in the current issue of the journal Current Opinion in Gastroenterology. The review includes the researchers' own findings concerning resistant starch and weight control. [The Scoop on 7 Perfect Survival Foods]

Starch vs. fiber

The word "starch" often is confused with fiber. Both are complex carbohydrates, and both are important for good health. But starch, for the most part, is highly digestible; and fiber is not. Starches are found in root vegetables, tubers, winter squashes, grains and legumes. Your body starts digesting these starches from the moment you start chewing, extracting nutrients and energy.

Fiber is more like the natural packaging for fruits and vegetables, such as the skin or the rigid cellular walls of plants. The human body does not absorb nutrients or energy from them. Soluble fiber dissolves in water, making food more viscous, slowing digestion, and prolonging the feeling of fullness. Insoluble fiber absorbs water and promotes regular and firm bowel movements.

Resistant starch has properties of both soluble and insoluble fiber, said Janine Higgins, lead author on the review paper and associate professor of Pediatrics at the University of Colorado School of Medicine. There are five different forms of resistant starch, she said, and each kind reaches the colon largely unscathed to do its handiwork.

Cures what ails you

Resistant starch might sound like some kind of miracle cure-all, but independent studies have found this substance, more so than ordinary dietary fiber, can help: kill precancerous polyps in the colon; prevent diabetes by improving insulin sensitivity and regulating blood sugar; maintain healthy body weight; reduce inflammation; prevent or treat inflammatory bowel disease; and help promote the growth of beneficial bacteria in the gut.

In 2010, scientists at Virginia Polytechnic and State University reported that resistant starch might also protect against breast cancer.

So, how can a bit of indigestible starch do all this?

"Resistant starch is a very good substrate for fermentation," Higgins told LiveScience. "Instead of being digested by amylases in the upper digestive tract, it passes to the bowel, where it is fermented by bacteria into short chain fatty acids (SCFA). SCFA are acidic, so they lower bowel pH, which facilitates proliferation of good bugs and inhibits growth of pathogenic bacteria. All of this extra fermentation and availability of SCFA provides fuel or energy for the colonocytes [cells lining the colon], which are a barrier against infection."

"Therefore, the lining of the bowel thickens and becomes healthier, and more good bugs colonize and thrive," Higgins added. "In this way, resistant starch acts as a probiotic. Resistant starch also has some of the properties of insoluble fiber, so it increases stool bulk and decreases transit time, both of which are indicators of bowel health."

Also, butyrate, a type of SCFA, seems to be involved in the prevention of bowel cancer, Higgins said.

Most high-fiber, vegetable-based diets will be rich in resistant starches, but some extra care is needed to get them into your diet. For example, pasta and rice have resistant starch, but only at room temperature. So, pasta salad and sushi are better sources of resistant starch. Whole grains, peas, and beans have a form of resistant starch that maintains its structure even when hot, though.

Green banana flour is another source of resistant starch, and it is gluten free.

Christopher Wanjek is the author of a new novel, "Hey, Einstein!", a comical nature-versus-nurture tale about raising clones of Albert Einstein in less-than-ideal settings. His column, Bad Medicine, appears regularly on LiveScience.